In internal combustions engines for motor vehicles including two-wheeled vehicles, the most important factor in getting the best performance from an internal combustion engine to respond to variations in required fuel injection amounts is to provide a suitable amount of fuel to the internal combustion engine at a suitable timing.
In an electronic fuel injection apparatus which injects fuel from a fuel injection nozzle, the fuel is controlled to a predetermined pressure using a fuel pump and a pressure regulator instead of using a carburetor. Properly controlling an operation time (nozzle open time) of the fuel injection nozzle enables accurate fuel injection control corresponding to required fuel injection amounts. Therefore, in recent years, particularly in four-wheeled vehicles, the electronic fuel injection system has been widely applied, substituting for the conventional carburetor system.
In the control of opening and closing a fuel injection nozzle, the nozzle is opened by applying a voltage to a solenoid coupled to the nozzle so as to inject the fuel, and is closed by interrupting the applied voltage so as to suspend the fuel injection.
FIG. 15 illustrates an example of a driving control circuit according to the conventional technique for driving a solenoid for fuel injection (hereinafter, referred to as a “solenoid” as appropriate) 11 in the aforementioned fuel injection apparatus. In the driving control circuit as illustrated in FIG. 15, a driving signal is input from an external control circuit (not shown), and when the driving level becomes a low level, an FET (Field-Effect Transistor) 12 coupled to the solenoid 11 turns ON, thereby starting the fuel injection.
In the example as illustrated in FIG. 15, the driving signal transmitted from the external control circuit is a pulse signal with continuous predetermined cycles, and the pulse signal turns ON and OFF repeatedly in a predetermined duty ratio (a ratio of ON time to a cycle). When the FET 12 is switched from OFF to ON, the power supply voltage, (for example, DC 12V) is applied to the solenoid 11, and a current starts to flow into the solenoid 11. Since the solenoid 11 is an inductive load, the current that passes through the solenoid (solenoid current) is zero at the time the FET 12 turns ON, and gradually increases for a period of time when the FET 12 is ON. Then, when the FET 12 is switched from ON to OFF, the solenoid current flows back to a fly-wheel diode 13, where the power is consumed and decreases gradually. At a time when the solenoid current decreases below a predetermined level, the fuel injection from the injection nozzle (not shown) is suspended.
However, in order to promptly respond to variations in required fuel injection amounts from the engine side, there is a case where it is necessary to hasten the decreasing time of the solenoid current subsequent to the FET 12 turning OFF so as to enable precise control of injection time. Therefore, in order to reduce the fuel injection duration time from the injection nozzle as much as possible after the FET 12 turns OFF, the solenoid 11 is provided with a variety of snubber circuits 14 as illustrated in FIGS. 16(a) to 16(d).
However, even when the driving circuit as illustrated in FIG. 15 is provided with a snubber circuit as illustrated in FIGS. 16(a) to 16(d), and a pulse signal is used as a driving signal which has continuous predetermined cycles and a predetermined duty ratio, since the current which passes through the solenoid 11 is a large current (of a few amperes), it is not possible to hasten the decreasing time of the solenoid current, and it is difficult to perform appropriate fuel injection having a quick response to rapid variations in required fuel injection amounts.
Further, when the solenoid current is dissipated simply as heat in the snubber circuit, corresponding to the dissipation, the energy efficiency of the entire engine system decreases and a battery with a greater capacity is required.
Recently, the inventors of the present invention have developed a fuel injection apparatus (hereinafter referred to as an “electromagnetic fuel injection apparatus”) using an electromagnetic fuel injection pump that pressurizes the fuel to be injected, as distinguished from the conventional type of fuel injection system that injects fuel that is pressurized with a fuel pump and regulator and then provides the fuel therefrom.
In the electromagnetic fuel injection apparatus, as distinguished from the conventional fuel injection apparatus, there are characteristics that the fuel injection amount is greatly affected by the solenoid current level as well as the solenoid driving time duration. Further, when a pulse width of the driving signal is wide, excessive currents flow into the solenoid, and current exceeding a level required for predetermined fuel injection are wastefully consumed. Furthermore, it is required to extremely shorten a pulse width during idle engine operation so as to secure a fuel injection amount at the time the nozzle is fully opened such as a time when the engine operates at high speed. However, there are limitations in decreasing a pulse width below a predetermined time duration due to issues such as inoperative time taken to start fuel injection after applying the voltage to the solenoid.
In view of the foregoing, it is an object of the present invention to provide a fuel injection control apparatus and fuel injection method which inject a suitable fuel having a quick response to variations in required fuel injection amounts from the engine side, while improving the energy efficiency, and particularly, to support an electromagnetic fuel injection apparatus.